1. Field of the Invention
The present invention relates to an apparatus for forming polymer continuously by DC plasma polymerization, and more particularly, to an apparatus used for the treatment of the surface of metal for thereby maximizing the utilization of a substrate by modifying the surface of the substrate or forming a new film material.
2. Description of the Background Art
Generally, when the surface of a substrate such as a metal plate is treated by plasma discharge, a coating layer having excellent hardness, abrasion resistance, etc. is formed. A product having the coating layer is used as a magnetic disk, optical disk, carbide tool, and the like. In addition, when a paint-coated film formed on the surface of a steel plate is plasma polymerized, the steel plate becomes hardened and has excellent durability and corrosion resistance.
Meanwhile, when it is made possible to continuously form polymer by plasma polymerization, the productivity of the polymerized product is improved. With regard to insulating materials including resin, fabric cloth, nonwaven fabric, etc. of a band-type substrate, it is relatively easy to continuously form polymer by plasma polymerization, and a number of apparatuses has already been proposed. (Japanese Patent 58-120859, 61-21105, and 2-103206).
However, in the case that the band-type metal used as the substrate is plasma polymerized by high frequency discharge while keeping it at an ungrounded potential, there is a problem in forming polymer continuously. The reason thereof is that since metal materials have conductivity, a discharge voltage is applied not only to an electrode, but also to the metallic substrate and metallic parts contacting the substrate. Thus, in the case that a metallic substrate is plasma polymerized by high frequency discharge while keeping it at an ungrounded potential, abnormal discharge occurs due to the conductivity of the metal and thus the apparatus is contaminated. In addition, the coated layer on the polymerized surface of the metallic substrate is apt to be powderized, or peeled off due to unstable discharge, resulting in degeneration of the coated layer and degradation of the product.
On the other hand, it is also possible to continuously form polymer by plasma polymerization while keeping a grounded potential. That is, the band-type metal material is plasma polymerized while keeping it at the grounded potential and continuously transporting the same. However, in the case that the grounded potential is kept, it is difficult to acquire deposition characteristics such as abrasion resistance which can be acquired in case of the ungrounded potential with respect to the plasma-polymerized substrate
In Japanese Laid-open Patent Hei 6-136506, an apparatus for forming polymer by plasma polymerization is disclosed. In the apparatus, a band-type substrate can be plasma polymerized by suppressing abnormal discharge and unstable discharge while keeping the above-mentioned ungrounded potential is disclosed. This apparatus makes it possible to generate plasma discharge under a predetermined pressure atmosphere and thus apply a discharge voltage only to electrode.
The apparatus comprises: a transport chamber 10 wherein a set of a unwinding roll 11 and a winding roll 12, a pair of tension rolls 13 and 14, and a support opening 15 are allocated; a deposition chamber 20 wherein deposition is performed on a substrate; a roll-shaped electrode 21 and an opposed electrode 22 allocated opposite to the roll-shaped electrode; an insulating shielding plate 30 prepared between the transport chamber and the deposition chamber; two differential openings 31 and 32 formed on the shielding plate for maintaining the pressure difference between the transport chamber and the deposition chamber; vacuum pumps 17 and 18 for controlling the pressure atmosphere of the transport chamber and deposition chamber; a gas injection opening 23 for injecting raw material gas into the deposition chamber; and exhaust openings 16 and 24 connected to the transport chamber and deposition chamber.
A substrate 1 to be plasma polymerized is transported from the unwinding roll 11 in the transport chamber 10, and is introduced into the deposition chamber 20 via the differential opening 31 at one side. Then, it is transported to the roll-shaped electrode 21, is passed through the vicinity of the opposed electrode 22, and thereafter is transported to the winding roll 12 in the transport chamber 10 via the differential opening 32 at the other side. In the above-described apparatus, in a process where the band-type substrate transported from the transport chamber to the deposition chamber is plasma polymerized by high frequency discharge and is send back to the transport chamber, the atmosphere of the deposition chamber is a glow discharge atmosphere, and the atmosphere of the transport chamber is a non-glow discharge atmosphere, which is lower than that of the deposition chamber.
Plasma discharge has a tendency to be generated under a predetermined pressure atmosphere according to the type of the discharge. For example, plasma polymerization is apt to be generated under a pressure atmosphere of 103xcx9c10 torr in general. Beyond this range, it is difficult to generate a glow discharge. Thus, even in the case that a band-type conductive metal material is polymerized, it is preferred that the transport chamber area and the deposition chamber are divided from each other, each of the areas is, maintained at a different pressure atmosphere by the differential opening, the deposition chamber is under the pressure atmosphere of 103xcx9c10 torr, and the transport chamber is under a pressure atmosphere beyond the above range, whereby, a glow discharge is generated in the deposition chamber while it is difficult to generate a glow discharge in the transport chamber, thus suppressing abnormal discharge.
Therefore, it is said that discharge is achieved not in the entire substrate, but in the deposition chamber alone by differentiating the pressure atmosphere of the chambers from each other as described above, whereby unpredictable discharge of metal materials excepting electrode portions is prevented with respect to the band-type metal substrate maintained at the ungrounded potential, thus forming a coating layer of a good film material.
However, in the apparatus, in a roll-shaped electrode as a discharge electrode and a curved opposite electrode as an opposite electrode are installed in the deposition chamber wherein plasma reaction occurs by high frequency discharge, and one surface of the substrate to be deposited is contacted by the roll electrode. In this case, of both surfaces of the substrate between the roll electrode and the opposite electrode wherein plasma reaction is actively occurred, deposition occurs only on the surface opposed to the opposite electrode, so there is an inconvenience of performing plasma treatment once more in order to deposit the other surface.
In addition, in the apparatus for forming polymer by plasma polymerization according to the conventional art, since discharge is achieved using high frequency power, (+), (xe2x88x92) power sources are alternatively applied to the substrate used as an electrode. At this time, in the case that the substrate is under the glow discharge atmosphere in case of (xe2x88x92), discharge tends to occur in the entire parts of the substrate irrespective of the position of the opposite electrode. The reason thereof is that discharge begins at the time when electrons are emitted from portions of a low potential.
In addition, in the apparatus for forming polymer by plasma polymerization according to the conventional art, in order that discharge is occurred only at a portion at which the opposite electrode is positioned, a differential opening is formed between the transport chamber and the deposition chamber, and the atmosphere of the transport chamber and the deposition chamber, are differentiated from each other, that is, the transport chamber is made to be under the ungrounded discharge atmosphere. In this case, a device for closing the gap between the chambers has to be added in order to prevent discharge from occurring on the entire substrate, and an additional vacuum pump is required in order to make each of the chambers vacuous by a set pressure. As a result, the number of parts to be put into installation is increased, thus causing the unit price of the apparatus higher.
Further, the electrodes in the deposition chamber has a predetermined area. In this case, carbonization of reaction gas occurs on the circumferential portions of the area of the electrodes, whereby deposition is non-uniformity formed to thus lower the uniformity of a plasma polymerized product.
In order to solve the above problems and efficiently obtain a good quality plasma polymerized film, an apparatus for forming polymer by plasma polymerization is provided. An object of the present invention is to acquire safety during the polymerization by insulating a main body from a substrate to which voltage is applied.
Another object of the present invention is to provide an apparatus for forming polymer continuously by DC plasma polymerization which makes it possible to deposit a high quality film by making discharge occur only in an opposite electrode portion without closing the gap between chambers by a differential opening, and which makes both surfaces of the substrate to be plasma polymerized at a time under the same conditions.
To achieve the above objects, there is provided an apparatus for forming polymer continuously by DC plasma polymerization according to the present invention, comprising: a transport chamber having an unwinding roll for unwinding a substrate to be surface treated and transporting the same to another chamber and a winding roll for winding the surface treated substrate; a deposition chamber for plasma polymerizing the surface of a substrate by DC discharge plasma by using the substrate as an electrode and installing an additional opposite electrode opposed to the substrate; a high voltage supply unit electrically connected to the substrate for applying a high voltage to the substrate; an insulating unit for electrically insulating an electrical path between the high voltage supply unit and the substrate from the main body of the apparatus; a pumping unit for maintaining a vacuum level of the deposition chamber; and a gas supply unit for introducing reactive gas and unreactive gas into the deposition chamber.
The substrate in the deposition chamber acts as an electrode, that is, an anode or cathode, by applying power to it. In the preferred embodiment, power is applied in such a manner that the substrate becomes the anode and the opposite electrode becomes the cathode.
The transport chamber can includes a unwinding chamber having a unwinding roll for unwinding the substrate to be surface-treated and transporting the same to the other chamber; and a winding chamber having a winding roll for winding the surface-treated substrate.
Between the transport chamber and the deposition chamber, an opening through which the substrate to be surface-treated or the surface-treated substrate can be freely moved is formed.
In the present invention, the power applied by the high voltage supply unit is applied to the substrate. Preferably, the substrate is used as an electrode by applying power to the unwinding roll or winding roll. In this case, an insulating member can be further included between the unwinding roll or winding roll and the chamber at a portion wherein the unwinding roll or winding roll is supported in the chamber. In addition, the substrate contacting the idle roller can be an electrode by applying power to the idle roller in the transport chamber.
In addition, in the apparatus according to the present invention, a plurality of electrodes can be installed at both upper and lower sides of the substrate in the deposition chamber, along the transporting direction of the substrate to be surface treated.
Further, the unreactive gas is introduced between the deposition chamber and the winding roll, and a post-processing chamber for performing after-polymerization on a polymerized substrate can be further included.